It is generally known to withdraw circular fabric from a circular knitting machine through delivery rolls positioned below the needle cylinder to flatten the same and then wind the flattened fabric onto a take up roll supported beneath the delivery rolls. The delivery rolls and the take up roll are supported in a frame which revolves with the needle cylinder. The revolving frame imparts rotation to a power transmission mechanism to impart rotation to the delivery rolls and the fabric take up roll. Various types of power transmission mechanisms have been proposed for imparting the proper speed of rotation to the delivery rolls and the fabric take up roll so that the fabric remains under tension as it passes through the delivery rolls and is wound on the take up roll.
The rotational speed of the delivery rolls is normally adjusted to be sufficient to maintain the fabric under tension when the knitting machine is set up to knit the maximum length of fabric. However, if the length of fabric being knitted is varied from this maximum length, because of different stitch construction, different types of yarn, or variation in the stitch length being formed, tension in the fabric will gradually increase during knitting to the point that the fabric is torn or knitting needles are placed under sufficient stress that breakage occurs. One proposed solution to such increased tension is to provide a detector to stop the knitting machine when the tension in the fabric increases above a predetermined amount. This stoppage of the machine requires attention by the machine operator to correct the problem and increases the cost of knitting the fabric.
Also, it has been proposed to support the delivery rolls on pivoted brackets so that the delivery rolls are raised by the fabric as the tension in the fabric increases. In this type of fabric take up, the power transmission mechanism includes fixed diameter drive pulleys connected by a drive belt and the upward movement of the delivery rolls decreases the distance between the drive pulleys so that the belt slips and rotation of the delivery rolls is temporarily stopped to reduce tension in the knit fabric. As the tension in the fabric reduces, the distance between the pulleys is gradually lengthened and the belt is tightened so that the delivery rolls are again rotated. With this type of take up mechanism, the tension on the knit fabric is constantly increased and decreased so that variable tension is continuously applied throughout the length of the fabric and this results in objectionable stitch loops of varying lengths in the fabric.
When it is desired to change the speed of the delivery rolls to knit different fabrics, it is necessary to manually change both of the drive pulleys for drive pulleys of different diameter. This is time consuming because the proper size of the drive pulleys is determined by trial and error. Also, this method of controlling the speed of the delivery rolls requires that a large inventory of different diameter drive pulleys be available for use.
It has also been known to utilize variable speed pulleys of the type having inwardly and outwardly adjustable tapered or cone-shaped drive flanges. With this type of drive pulley, the speed of rotation imparted to the delivery rolls and the fabric take up roll by the power transmission mechanism can be varied, relative to the rotational speed of the needle cylinder. In this type of variable speed pulley arrangement, the radial position of the belt contacting the inwardly tapered pulley flanges is varied to match the rotating speed of the take up mechanism with the knitting speed so that the drive pulleys do not have to be manually changed. However, this arrangement does not permit slipping of the belt when an abnormal amount of tension is placed on the knit fabric so that there is danger of the fabric being torn or the needles being broken.